Orion with the service module has a dry weight of 26 tons, the Apollo CSM weighed 12 tons, according to Wikipedia. Will SLS have capacity to squeeze in a Lunar lander with ascent vehicle and a habitat for, say, three astronauts during two weeks? Isn't Orion too big to function as a CSM?

So with an Orion crew of 6 the capsule dry mass per crew member is 1648 kg and with a crew of 3 the Apollo CM dry mass per crew member is 1947 kg. Orion saves 299 kg per crew member, or (299 / 1947) = 15%.

So with an Orion crew of 6 the capsule dry mass per crew member is 1648 kg and with a crew of 3 the Apollo CM dry mass per crew member is 1947 kg. Orion saves 299 kg per crew member, or (299 / 1947) = 15%.

Is that correct and fair?

Not really.

Apollo was designed for a mission crew of 3, but could have as many as 5 in the Skylab Rescue version.

Orion is designed for a mission crew of 4, but could have as many as 6. Since it is bigger than Dragon or Starliner which can hold up to a crew of 7, you could probably get even more astronauts in an Orion if you wanted.

Orion needs more volume per crewperson because of longer missions (21 days instead of 14 days), so that makes direct comparisons difficult.

Um? What size crew do you think NASA is planning to send on Mars missions?

Well, we're getting a bit side tracked since this is the Lunar thread, but NASA had planned on sending six crew in previous Design Reference Missions (DRM). I think the current plan though is sending four crew. That's how many crew fit in the Exploration Augmentation Module (EAM).

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Akin's Laws of Spacecraft Design #1: Engineering is done with numbers. Analysis without numbers is only an opinion.

Um? What size crew do you think NASA is planning to send on Mars missions?

What does that have to do with the Orion? It can only land in Earth's oceans, and Steven Pietrobon here says that it is too small to be used as Apollo's CSM. So I don't understand what it has been designed for, it seems to be completely useless by design.

Um? What size crew do you think NASA is planning to send on Mars missions?

What does that have to do with the Orion? It can only land in Earth's oceans, and Steven Pietrobon here says that it is too small to be used as Apollo's CSM. So I don't understand what it has been designed for, it seems to be completely useless by design.

Orion can do lunar missions with a crew of four. Orion can be used as a taxi on Mars missions with a crew of six. As the Mars ship stack loops around to go back to L2, Orion reenters with the crew. Probably better ways to do that.

SLS 1B is just too small and Orion is just to big and heavy for any significant co-manifested Lunar Lander.

But a SLS 2 130mt may be big enough if the prop used on the lander is hydrolox not storable prop. SLS 2 would have only a capability of < 25mt for a co-manifested payload. The other additioanl problems is that the SM must be larger than current as well which then eats into this value too.

Remember the Constellation was estimating that a hydrolox =co-manifested lander with Orion would need a 200mt launcher. SLS 2 would still be 50mt or more under performing for a true Lunar surface co-manifestied lander capibility. You would have to drastically do weight reductions and other limitations to do a co-manifested Lunar surface mission.

The numbers just do not support it.

With a different much lighter crew capsule probably but not with an Orion.

IMHO Use separate launches to send a reusable lander, a lunar orbit space station with hanger for the lander and a SEP tug to deliver propellant plus other consumables. Then further landings just need to send the Orion with crew and a few supplies.

IMHO Use separate launches to send a reusable lander, a lunar orbit space station with hanger for the lander and a SEP tug to deliver propellant plus other consumables. Then further landings just need to send the Orion with crew and a few supplies.

Yes. There is no need to think in terms of single-flight missions as with Apollo, and that is booster-agnostic.

I would add a surface habitat delivered on one unmanned flight, so the reusable lander can be even smaller. Or two flights: one to put the hab in lunar orbit, and a second carrying a bare-bones lander to take it down to the surface.

IMHO Use separate launches to send a reusable lander, a lunar orbit space station with hanger for the lander and a SEP tug to deliver propellant plus other consumables. Then further landings just need to send the Orion with crew and a few supplies.

Yes. There is no need to think in terms of single-flight missions as with Apollo, and that is booster-agnostic.

I would add a surface habitat delivered on one unmanned flight, so the reusable lander can be even smaller. Or two flights: one to put the hab in lunar orbit, and a second carrying a bare-bones lander to take it down to the surface.

The thing is, none of this can work if SLS flies only once a year.

If the SEP tug is launched using a different type of launch vehicle there can be a manned landing within a 3 year period and a base in 4 years using launch one a year SLS.

Any lunar missions using SLS/Orion are likely to stage from DSH and will require to launchers. One launch to deliver lander to DSH and another for crew. Return trip of approx 5km/s from DSH to surface is big ask of lander but possible.

Apple with oranges here. The Saturn V payload (nominally 118 t) does not include the S-IVB. The SLS IB payload includes the Exploration Upper Stage (EUS) mass of 11.9 t.

Apples (including upper stage)Saturn V 140 tSLS IB 105 t

Oranges (without upper stage)Saturn V 118 tSLS IB 93.1 t

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But a SLS 2 130mt may be big enough if the prop used on the lander is hydrolox not storable prop. SLS 2 would have only a capability of < 25mt for a co-manifested payload. The other additioanl problems is that the SM must be larger than current as well which then eats into this value too.

I'm not sure that would work with 130 t. A hydrolox descent stage is very mass inefficient. With 140 t of true payload mass, I was able to get it to work using staged descent with a cryogenic propulsion stage (CPS). See my paper "Fly me to the Moon on an SLS Block II". If the Descent Stage or CPS performs low Lunar orbit (LLO) insertion, Orion has enough delta-V for Trans Earth Injection (TEI).

In an alternate timeline the Apollo missions became multiple launch missions with the LM modified as a lander only and delivering the longer stay hab in place of the ascent stage. The 2 stage LM became a taxi and longer missions centering around a base camp became possible. Going forward, this is how we should set up lunar exploration. With the modern addition of a re-usable lunar taxi. SLS could play a role in delivering the surface hab. It could play a role in delivering the orbital station. As these other programs come on line (New Glenn, etc.), the role of SLS would be diminished in this arena, but might soldier on for a time delivering components for the Mars transfer ship. SLS is probably a short term bridge as we ramp up to the next phase of space exploration.